Power is generated at power plants and distributed to customers through a network of power plants, transmission lines, substations, and distribution systems. For example, in the case illustrated in FIG. 1, power is generated at a Power Plant A 10 and a Power Plant B 12 and transmitted to a substation 14 through high-voltage transmission lines 16. The high-voltage transmission lines 16 form part of a power grid that connects power plants and substations across a wide area. At the substation 14, power is “stepped down” in voltage and eventually supplied to various end users 18 (e.g., residences and businesses) through distribution transformers 19 that are located near the end users 18. The distribution transformers 19 are organized by feeder circuits (group of power lines) that transmit power from the substation to the individual transformers 19. At least one feeder circuit comes out of each substation 14, and each feeder circuit feeds one or more transformers 19. The distribution transformers 19 step voltage down to a line voltage, which is a step down of between about 4 kV and 34 kV.
The distribution transformers are sized to comfortably meet the expected maximum peak load. Although this “oversizing” of transformers comes at a price, this price is a relatively cheap insurance against outages that can result if transformers are overloaded.
FIGS. 2A and 2B illustrate the effect of excess-capacity loading on the lifespan of a transformer. If a transformer were operated continuously at the nameplate capacity and rated ambient conditions, its typical expected lifespan is about 10–20 years. However, if a transformer load exceeds capacity even for a few hours on a few days of the year, the transformer can suddenly fail long before the expected lifespan is reached. FIG. 2A shows the temperature fluctuations between about May 2001 and August 2001, and illustrates how transformer load correlates with outdoor temperature. In late July/early August, when the temperature exceeded 80° F., the transformer load exceeded 100% of the load capacity. As shown in FIG. 2B, the consumed life of the transformer during this period increased dramatically, from about 500 hours to about 1,400 hours. Due to this sensitivity to excess loading, a transformer experiences almost all of its annual “aging” in a relatively small number of overload events.
Accelerated aging of the transformer leads to an earlier failure of the transformer, usually at an unexpected time. Typically, about 1% of transformers fail unexpectedly in a given year. While this relatively small number may appear to be an acceptable risk, the location of such failures is difficult to predict and their timing is often coincident with other problems typical for a peak day. The replacement is costly in terms of labor that must be rushed to the site as well as fines that may be levied by the PUC in some states. Failure of a transformer can also incur non-monetary costs, such negative effects on public relations.
These costs can be dramatically reduced by a reasonably accurate prediction on transformer failure. Thus, a method and system for predicting transformer failure could be extremely beneficial to various entities in the power supply chain, for example to utility companies.